The goal of this research is to contribute to the understanding of the biochemical mechanisms of plaque formation and periodontal disease induction in man. The biosynthesis of plaque-forming polysaccharide will be studied in Actinomyces viscosus, a human oral bacterium which forms plaque and which produces periodontal disease in experimental animals. This study deals specifically with the biosynthesis of levan by this organism. Enzyme in the growth medium of A. viscosus incorporates the fructose moiety, but not the glucose moiety, of labelled sucrose into high molecular weight polymer. A levansucrase has been purified to homogeneity from the growth medium (trypticase soy broth). The enzyme has a specific activity of 89 micron moles of glucose liberated from sucrose per minute per mg of protein at 25 degrees ,pH 7.5, in a spectrophotometric coupled enzyme assay containing 50 mM sucrose. When the purified enzyme is added to a sucrose solution, a turbid precipitate of levan forms. The purified enzyme will be characterized with respect to molecular weight, subunits, amino acid and carbohydrate composition, and cofactor requirements. Various agents, such as sucrose analogs, will be tested to block induction and to inhibit levansucrase activity. The levan product will be characterized with respect to molecular weight distribution and sugar linkages. With knowledge of the properties and regulation of the levansucrase of A. viscosus, it may be possible to suggest ways of regulating this activity, in vivo. This, in turn, may suggest strategies for the control of plaque formation and the prevention of periodontal disease in man.